When Occupy Wall Street and similar protests played out over the past year, the phenomenon looked familiar to Emory University primatologist Frans de Waal: He's seen similar moral outrage over economic inequity expressed by monkeys and chimps. And he thinks we could learn a lesson or two from our fellow primates.

"The role of inequity in society is grossly underestimated," he told reporters today, on the final day of this year's meeting of the American Association for the Advancement of Science in Vancouver, Canada. "Inequity is not good for your health, basically."

Based on primate studies, that goes for the haves as well as the have-nots. Far from being a uniquely human quality, a sense of fairness is something biologists have seen in studies of primates as well as crows and dogs. Even elephants may have an appreciation of inequity, although de Waal said he and his colleagues haven't done such a study with that species because "you don't want to piss off an elephant."

One of the classic studies involves capuchin monkeys who were given treats when they exchanged tokens with their human handlers. Two types of treats were offered: cucumber slices (meh...) and grapes (yum!). If one monkey saw that another monkey was consistently getting grapes while she was getting only cucumber slices, she'd quickly start protesting — by flinging the cucumber back at the handler and angrily jumping onto the cage walls.

"This is basically the Wall Street protest right here," de Waal said.

De Waal's replay of the scene never fails to get a human laugh, whether it's at the AAAS meeting or at a TEDx conference in Atlanta, as shown in the must-see video above. But there are serious points behind the laughter: Inequality causes tension and stress, not only for the one who gets the cucumber, but also for the one gets the grape (or a million-dollar bonus) and has to endure the resulting outrage.

Researchers set up a barter game with capuchin monkeys to see how they responded to unequal payoffs. For the full story behind this experiment, check out the NSF Science Nation video.

Some primates actually get the message. "In some combinations, the one who gets the grape refuses it unless the other one gets the grape," de Waal said. Other primates make a different choice. De Waal pointed to a chimpanzee study of selfish vs. altrustic behavior, in which the chimps are more likely to be in a sharing mood if they've attracted the attention of another chimp. However, they're not quite as likely to share if the other chimp is actively pressing them to do so.

The bottom line from de Waal's talk is that a sense of fairness, outrage over moral equality and the ability to reconcile and cooperate are not uniquely human behaviors. Rather, such sensibilities were hard-wired into brains long before the rise of the human species. This is reflected in neuroscience as well, de Waal said. "Very ancient parts of the brain are involved in moral decision making," he observed.

All this meshes with the message of de Waal's latest book, "The Age of Empathy." For more from de Waal about the altruism of animals, check out my Q&A from 2009.

Here are a few more nuggets from de Waal's lecture and news briefing in Vancouver:

Different primate species express signs of reconciliation in different ways. For example, stumptail monkeys make up by inspecting each other's rear ends, without ever looking each other in the eye. In contrast, chimps and other apes (including us hairless apes) "need eye contact" when they reconcile their differences, de Waal said.

Empathy — the ability to share an emotional connection with other individuals — isn't unique to humans. But humans, like many other species, make a distinction between in-group and out-group connections. Having a sense of empathy for people beyond our "in-group," however that's defined, may be a "fragile experiment" being conducted by our species, de Waal said.

During an earlier session at the AAAS meeting, a group of scientists and philosophers called for the promulgation of a "Declaration of Rights for Cetaceans." De Waal was asked what he thought of setting up a declaration of rights for non-human primates, and he replied that he generally took a "welfarist" view toward other species. Humans were bound by an obligation to animals rather than by a set of rights drawn up on their behalf, he said. He pointed to the recently adopted limits on chimpanzee research as an example. "If they [chimps] are not so necessary for biomedical studies, should we be using them in biomedical studies?" de Waal asked.